Incandescent Bulb "Wear Out"

jeff_wisnia · 2013-02-04T18:05:25+00:00

I hadn't thought much about this before but today I started wondering what percentage of light output is typically lost as a large (100-250 watt) incandescent bulb ages, before it's filament finally fails.It seems to me that the noticeable deposits on the inside of the glass bulb must block some light, and as the filament boils off some of it's tungsten its resistance must increase, so the power dissipated in it will drop, reducing the light output.Or, maybe it's just my aging eyes. Jeff

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Tomsic 13 years ago

Yes, certain bulbs will blacken much faster than others. Vacuum bulbs, which are usually the small low-wattage types, get black very fast. Gas-filled bulbs blacken more slowly because the pressure of the gas slows down the escape of tungsten from the filament. The Lighting Handbook says that a gas-filled bulb will have an average light loss of 15% and end up with a light output 20% below initial. Halogen bulbs recycle the filament particles that burn off, so their average loss of light is about 5% and only

6% at end-of-life.

Wall-box electronic dimmers - even when set at full output - don't operate the bulb at full voltage. There is a few volts drop just because of the circuit, but I've heard dimmer manufacturers say in meetings that some dimmers are designed with a 10% drop to lengthen bulb life. I've never checked that, however. Does anyone have voltage data that they might share?

Tomsic

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bob haller 13 years ago

rote:

I reported a safety hazard to UL once, basically they didnt care, and I am a dealer for the product and could of been killed.....

I also found a wiring misake in a machine that neither the manufacturer or UL cared about:( They fused the white neutral side of the power line. A real hazard if the machine blows a fuse, wth the fuse on the white neutral power line side someone could get shocked or killed by a machine with the main fuse blown:(

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Tomsic 13 years ago

I reported a safety hazard to UL once, basically they didnt care, and I am a dealer for the product and could of been killed.....

I also found a wiring misake in a machine that neither the manufacturer or UL cared about:( They fused the white neutral side of the power line. A real hazard if the machine blows a fuse, wth the fuse on the white neutral power line side someone could get shocked or killed by a machine with the main fuse blown:(

Sad - no excuse for it. I've found both UL and CSA responsive; but I deal with them more on the testing side than the user side. Wonder if a call to the local electrical inspector might have helped.

Tomsic

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bob haller 13 years ago

Since I was a dealer for the manufacturers involved I didnt want to create a big stink, but was amazed UL wasnt interested, and on the safety issue that endagered users I contacted them twice and got the same brush off both times.....

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danny burstein 13 years ago

In the Good Old Daze (1975) I had a spec booklet from GE that had exctlty that info for their incandecent and other lamps. It also had a diagram showing the surface temperatures in different positions and locations.

But try finding that today....

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jeff_wisnia 13 years ago

That sounds correct to me. When we built our home some 27 years ago the four 25 watt "vanity" bulbs across the top of our main bathroom's mirror/medicine cabinet were a bit too bright for my taste.

I put a variable dimmer in a box inside the top of the cabinet with its knob shaft sticking up through the top of the cabinet where it's out of sight to anyone less than 7 feet tall.

I cranked the dimmer down a bit until the brightness was comfortable, and to this date all four of the original bulbs are still working fine.

And, just last nite the 150 watt incandescent bulb in the end table lamp I read by burned out on turn on and after I replaced it there was noticeably more light. It would have been fun to anticipate that and have a light meter handy to check the difference, but I haven't had one of those in about 50 years now, ever since cameras had them "built in" in one form or another.

Jeff

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